Sealing rings are commonly used to seal pipe joints such as a bell and spigot joints in a pipe line. Lubricants such as a soap and water solution can be manually applied to the sealing rings to reduce the friction forces during the joining of two pipes. This is time consuming and messy work.
Self-lubricating sealing rings have been developed to avoid the manual labour involved in applying lubricant to a sealing ring and to expedite the process of joining two pipes.
U.S. Pat. No. 5,143,381 which issued Sep. 1, 1992 to Temple, discloses a sealing ring which has a closed chamber storing a lubricant such as grease. The sealing ring is placed upon the spigot end of a first pipe. The bell-shaped end of a second pipe engages the closed chamber and rolls back a flap formed in the sealing ring to open an annular slit thereby exposing a lubricant contained therein. In that the flap must be displaced onto the outer periphery of the ring, the thickness of the flap causes an undesirable radial pressure on the bell-shaped end of the second pipe.
U.S. Pat. No. 4,934,716 which issued Jun. 19, 1990 to Nordin et al., shows a sealing ring having a membrane attached to a substantially triangular body. The base of the triangular body of the sealing ring is placed on the spigot end of a first pipe. When the bell-shaped end of a second pipe is fitted onto the spigot end of the first pipe, it comes into contact with the membrane and slides along the membrane. At the same time, the membrane slides upon the triangular body. There is little frictional resistance between the membrane and the sealing ring due to the presence of a lubricant disposed therebetween. The membrane extends beyond the vertex of the triangular body when the seal is effected, necessitating the presence of an annular space to receive the thickness of the membrane doubled upon itself.
Sealing rings are usually comprised of rubber and extrusion is the most common method of forming rubber sealing rings. It is difficult to extrude rubber sealing rings with a thin membrane. The thinnest rubber membranes which may be formed by extrusion cause problems with the joint of existing pipes. Since the membrane extends beyond the vertex of the body of the sealing ring, when using sealing rings produced through extrusion such as those disclosed in U.S. Pat. No. 4,934,716, it affects the fitting of the joint. These products require the bell and spigot ends of two adjoining pipes to be machined to provide a wider joint than normal to allow for usage of these sealing rings.